The present invention relates to a level adjustment device and method capable of automatically adjusting a volume level of a sound signal such as a music sound signal to a proper volume level in such a case that a currently played music is changed to another one in background music, or the volume level is varied in a currently played music, for example.
In a case that a plurality of music pieces are played continuously via an audio system as background music or the like, because of a difference of volume levels between the music pieces played one after anther and/or a level variation in a currently-played music piece, it is desired to automatically adjust volume levels of musical sounds being played to proper volume levels for each music piece so that a listener can hear surely the musical sounds, and that the volume levels do not become louder. To automatically adjust the volume, there have been known a level adjustment device which controls an audio gain in response to a level of an input signal so as to suppress the level variation in the input signal and outputs the gain adjusted output signal. Such the level adjustment device comprises a level detection section to detect a level of an input signal. This level detection section is constructed to detect the level of the input signal following a level variation in the input signal, and a following rate therefor is decided according to a time constant which is variably set in the level detection section. If the following rate is set to a low rate by setting the time constant to a great value, the level detection cannot follow a level variation in a time period where the level of musical sounds varies at high rate, therefore the level of the musical sounds played in the time period will be too loud. On the other hand, if the following rate is set to a high rate by setting the time constant to a small value, because the level adjustment will follow rapidly the variation of the level of the musical sounds, a listener will perceive the variation of the gain level. Accordingly, there have been proposed a level adjustment device constructed to calculate a long-term gain corresponding to a low following rate and a short-term gain corresponding to a high following rate, and to adjust the level of signals based on the calculated long-term gain and short-term gain (see Japanese Patent No. 5236006 which corresponds to U.S. Patent Application Publication No. 2011/255712, for example).
From a standpoint of a listener, perceiving the gain variation during a playback of a music piece is undesirable because of disturbing music listening. That is, it is desirable to slow the following rate for the gain adjustment, basically. However, the conventional method which calculates both of the long-term gain and the short-term gain has a complicated construction of signal processing. Further, it is difficult to predict how the level of the signal varies after the gain adjustment.